This invention relates to filters, and more particularly to apparatus for filtering fluid media, of the type having a first chamber provided with an inlet, a second chamber provided with an outlet, and ports disposed between the first and second chambers and provided with a filter fabric through which the medium to be filtered flows.
An apparatus of the foregoing type is particularly suitable for filtering high-viscosity media, especially such as tend to settle out, coagulate, crystallize, or gelatinize, or suspensions which tend to settle out in dead angles, which presents a well-known problem in the food industry.
An apparatus of this type has already been proposed. U.S. Pat. No. 3,994,810, for example, discloses such an apparatus having a cylindrical first chamber to which the medium to be filtered is conveyed via an inlet. The wall of the cylindrical first chamber includes ports behind which the filter fabric, likewise substantially cylindrical, is disposed. The cylindrical filter fabric is surrounded by a second chamber having an outlet.
The medium to be filtered flows via the inlet and the first chamber through the ports in front of the filter, penetrates the latter, and reaches the outlet via the second chamber. It has been found, however, that the medium does not flow uniformly through the filter since it takes the path of least resistance, namely the direct path between the inlet and outlet connections. In the areas through which less medium flows, deposits are formed, or the medium coagulates. This results in a loss of active filter surface.
Depending upon the production conditions, the discharge may vary. It has been found that with a small volume of flow, the area in which coagulated medium is deposited becomes larger.
When the discharge is increased, these deposits are broken up again. Part of the decomposed material then flows along once more in the stream of filtrate as a contaminant and can lead to malfunctions in subsequent further processing steps.
Another problem arises from the use of the perforated supporting pipe. Medium flows properly through the filter rings merely in the region of the perforations. This causes the occurrence of current shadows in which the medium may coagulate. The solids thus deposited cannot be broken up again by backflushing. The result is a significant loss of active filter surface.
There are also other prior art devices for filtering fluids which are constructed similarly to the aforementioned apparatus. Here the filter fabric is stretched directly over a perforated pipe. In this case, the filter fabric is inflated like a balloon during the filtering operation, so that it is lifted off the supporting pipe. It is then possible for solids to accumulated between the non-perforated region of the supporting pipe and the filter fabric. During backflushing, the filter fabric is flattened against the supporting pipe again, whereupon the deposited solids are pressed into the filter fabric. They can no longer be removed by means of backflushing. Demanding and expensive heat treatments are then required for cleaning the filter fabric.